This invention relates to digital communications systems wherein multiple data lines are coupled to various circuit modules and, more particularly, to an arrangement for determining the presence or absence of signals on each data line.
The communications industry requires reliable operation over long periods of time and to this end, reliable self diagnostic equipment or circuits are required to monitor the validity of data entering and leaving functional blocks. Circuits and systems are known for determining the presence or absence of data on transmission lines. However, such known circuits utilize large numbers of circuit modules and the resulting systems are undesirably complex and expensive.
Accordingly, it is a primary object of this invention to provide an improved system and circuit for determining the presence or absence of data on transmission lines.
Another object of this invention is to provide an improved system for sensing data on transmission lines with an economy in the number of circuit elements and power required in the system.